An optical disc is an electronic data storage medium that can be written to and read from using a low-powered laser beam. For example, a CD (compact disc) is typically used to record, store, and play back various media such as audio, video and text in digital form, while a DVD (digital versatile disc) is generally used for storing and playing back whole movies due to its increased storage capability.
Recordable and rewritable disc drives for both CDs and DVDs have become common place, enabling the average consumer to record and rewrite their own data onto their own CDs and DVDs by “burning” the data into, for example, CD-Rs (CD-recordable discs), CD-RWs (CD-rewritable discs), DVD+Rs (DVD-recordable discs), and DVD+RWs (DVD-rewritable discs). The ability to create personalized collections of data on CDs and DVDs has driven consumer desire for convenient ways to identify the data in such collections. Accordingly, methods for labeling the non-data side of optical discs (e.g., CDs, DVDs) have developed from physically writing on the non-data side of a disc with a permanent marker, for example, to using the laser in a conventional CD player to mark a specially prepared CD surface.
In general, a label image can be rendered on the label surface of an optical disc (i.e., the non-data side, or top side) by marking the label surface with a laser beam along concentric circles around the disc. For each circle, spots of constant size and optical density are marked by the laser according to marking data for that circle. However, because there are typically no markings or other reference points on the non-data/label side of a disc, accurately positioning the laser in the radial direction of the disc has remained a challenging problem.